This application claims priority under 35 U.S.C. xc2xa7xc2xa7119 and/or 365 to Appln. No. 01810560.1 filed in Europe on Jun. 11, 2001; the entire content of which is hereby incorporated by reference.
The present invention relates to the field of insulation and electrical conductor technology. It relates in particular to an insulator for an electrical busbar system, as well as an insulator system having at least two such insulators, as claimed in the precharacterizing clause of the independent claims.
Nowadays, insulators for electrical busbar systems are used in a wide range of power-electronic circuits, in particular in converter circuits, for insulating live rails from one another and from ground potential. Normally, such an electrical busbar system has at least one rail which carries an electric current and whose voltage potential is not ground potential. In a busbar system having two or more rails, the individual rails are at different voltage potentials. The rails are routed close to one another in order to provide a low-inductance connection, for example between the circuit breakers in a converter circuit and an energy store for this converter circuit, in particular a DC intermediate circuit, with known insulators being used to insulate them from one another and from ground potential. One such insulator is in the form of an axially symmetrical insulator body which has a hole along the direction of the axis of symmetry. Furthermore, a mounting surface which is vertically at a distance from the hole and extends radially as far as the rim region of the body, is provided on each of the end faces of the body with respect to the axis of symmetry, in order to make flat contact with a rail. Furthermore, the body has a multi-part construction composed of insulator body parts, which are stacked in the direction of the axis of symmetry. This results in a sufficiently long creepage distance in the direction of the axis of symmetry to provide insulation between two rails. Each insulator body part is formed from a multilayer, in particular glass-fiber-reinforced, insulation material, such as HM35.
One problem with a multipart design such as this is that a large number of insulator body parts are required to achieve a sufficiently long creepage distance in the direction of the axis of symmetry. A body such as this formed from insulator body parts requires a considerable amount of space, however, and is susceptible to mechanical influences, in particular bending stresses, transversely with respect to the direction of the axis of symmetry. Such mechanical influences occur, for example, in the event of a current surge on a live rail which is routed close to another rail or close to ground potential and is separated by the body from the other rail or the ground potential. This can result in partial discharges between the insulator body parts and in flashovers between the rails, or between one rail and ground potential, in which case the body may be damaged or destroyed. The insulator then no longer ensures that a sufficient amount of insulation is provided. Furthermore, the multi-part design of the insulator described above is highly intensive in terms of assembly and maintenance.
Normally, a ground potential rail runs through the hole in the body. In order to achieve a sufficiently long creepage distance between this ground potential rail and a rail located on the mounting surface, a cutout is provided in the direction of the axis of symmetry in the rail resting on the surface, which cutout is many times larger than the hole in the body, in order to maintain the creepage distance which is required for insulation between the rail resting on this surface and the ground potential rail. When a high power level is to be transmitted via such a rail, however, the rail must be designed to have a very large area in order to allow it to carry the high current associated with the high power level. However, a rail designed in this way occupies a large amount of space, uses a large amount of material, and is thus expensive. Furthermore, a rail designed in such a way requires a number of insulators alongside one another, thus resulting in further material costs, in particular component costs.
In addition, the insulator described above is not suitable for forming an insulator system from a number of bodies, since the mechanical influences which occur as mentioned above can lead to the insulator system not being mechanically robust, in which case the insulator system may be damaged or destroyed. Furthermore, an insulator system formed from a number of insulators as described above requires a considerable amount of space.
One object of the invention is therefore to specify an insulator for an electrical busbar system having at least one rail, which insulator is distinguished by providing a high level of insulation while being resistant to partial discharges and flashovers, and which has a particularly simple, robust design, which is space-saving, and hence is cost-effective. Another object is to specify an insulator system which comprises at least two insulators according to the invention, has a space-saving design, and is very largely resistant to mechanical influences. These objects are achieved by the features of claims 1 and 9. The dependent claims specify advantageous developments of the invention.
The insulator according to the invention is in the form of an axially symmetrical body and has a hole along the axis of symmetry, with a mounting surface, which is vertically at a distance from the hole and extends radially as far as the rim region of the body, being provided on each of the end faces of the body with respect to the axis of symmetry, in order to make flat contact with one rail in the busbar system. According to the invention, the body is formed integrally, as a result of which the body advantageously has a very high level of intrinsic mechanical robustness, so that mechanical influences such as those which occur in the event of a current surge in a live rail which is resting on the mounting surface and is routed close to another rail or close to ground potential have virtually no influence on the insulator. Partial discharges on and in the body as well as flashovers between rails or between one rail and ground potential can thus be successfully prevented, so that the insulator provides a high level of insulation.
Furthermore, according to the invention, an essentially ribbed first surface extends in the radial direction between the hole and the mounting surface. A cutout which is normally provided on a rail resting on the mounting surface can advantageously be chosen to be small, since the creepage distance (which is required for insulation) between the rail resting on this surface and a ground potential rail (which normally runs through the hole) is achieved via the ribbed first surface. The end faces of the body of the insulator and the rail resting on it can thus be designed to be highly space-saving in terms of the area, and hence cost-effective, particularly when a high power level is to be transmitted via such a rail. Furthermore, this makes it possible to produce a light insulator, which uses little material and is thus cost effective.
In the insulator system according to the invention, at least two insulators according to the invention are provided, whose bodies are arranged to be aligned in the direction of the axis of symmetry and form a stack. Furthermore, one of the mounting surfaces of in each case two adjacent bodies is pressed against a rail which is arranged between the two bodies. This results in the insulators in the insulator system forming an extremely compact assembly, which is intrinsically highly robust and is largely resistant to mechanical influences. Furthermore, the aligned arrangement of the bodies of the insulators results in the insulator system having a highly space-saving design. In addition, the first surface of each body of the associated insulator can advantageously be protected against dirt and environmental influences.
These and further objects, advantages and features of the present invention will become evident from the following detailed description of preferred exemplary embodiments of the invention, in conjunction with the drawings.